Wiring structure forming method and semiconductor device

ABSTRACT

After a via hole to connect a lower wiring and an upper wiring not shown is formed in an insulating film using an etching stopper film and a hard mask, a base film made from tantalum is formed on the insulating film so as to cover an inner wall of the via hole by a one-step low-power bias sputtering method of the present invention. Thus, the base film with a thin and uniform film thickness covering a region from an inner wall surface of the via hole to the insulating film is obtained.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-003383, filed on Jan. 8, 2004, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wiring structure forming method in which a conductive material is embedded in an opening formed in an insulating film above a substrate, and a semiconductor device, and particularly it is technology suitable for application to a so-called damascene method in which Cu wiring is formed with an opening as a minute wiring trench or connection hole and with Cu (alloy) as a conductive material.

2. Description of the Related Art

With high integration of a semiconductor element and a reduction in chip size, finer wiring and multilayered wiring are acceleratingly promoted. In a logic device having such a multilayer wiring structure, wiring delay is becoming one of factors governing device signal delay. The device signal delay is proportional to the product of wiring resistance and wiring capacity, and hence, to improve wiring delay, reductions in wiring resistance and wiring capacity are important.

To reduce the wiring resistance, the formation of wiring with Cu which is low-resistance metal as a material is studied. Since it is very difficult to form wiring by patterning Cu, a so-called damascene method in which an opening which becomes a wiring trench or a connection hole (via hole) is formed in an insulating film and filled with Cu to form the wiring is worked out.

When Cu wiring is formed by the damascene method, a step of forming a base film which covers an inner wall of the opening before Cu is deposited is included, mainly in order to prevent Cu from diffusing into the insulating film. Refractory metal such as Ta or W used as a material for the base film is generally high resistant. In recent years when finer wiring is promoted, it is indispensable to reduce the resistance value of the base film from a matter of wiring resistance. In particular, in the case of an ultra-fine wiring layer containing a via hole with a diameter of 0.1 μm and a wiring with a width of 0.1 μm, it is necessary to thin the base film as much as possible in order to reduce wiring resistance and contact resistance, and hence the technology for forming a base film thin and uniformly on an inner wall of a wiring trench or a via hole is desired.

A CVD method is first thought of as a method for forming such a base film. As far as the formation of the thin and uniform base film is concerned, it is thought that the use of the CVD method is advantageous, but the CVD method has a big problem in compatibility with and adhesiveness to a low dielectric constant insulating material which is expected as a material for the insulating film in which the opening is formed, and the application of this method is difficult in the present circumstances. A sputtering method is superior in the aforementioned compatibility and adhesiveness to the CVD method, whereby the use of the sputtering method for the formation of the base film is considered to be suitable.

At present, as sputtering technology used for forming the base film, there are a long throw sputtering method in which the distance between a substrate and a target is set longer than normal, a bias sputtering method in which a film is formed while a bias voltage is applied to a substrate, a multistep sputtering method in which two or more steps of sputtering as a combination of sputter deposition and sputter etching are performed, and so on.

-   -   (Patent Document 1)     -   Japanese Patent Application No. 2002-318674

However, under the present circumstances, even if the aforementioned various methods are used, the base film cannot be formed thin and uniformly on an inner wall surface, that is, from a side wall surface to a bottom surface, of the wiring trench or the via hole.

Specifically, part of a process of forming wiring containing a base film is shown in FIG. 7A and FIG. 7B, and FIG. 8. Here, for example, when a via hole 102 to connect a lower wiring 101 and an upper wiring not shown is formed in an interlayer insulating film 103 using an etching stopper film 104 and a hard mask 105, a Ta base film 106 is formed on the interlayer insulating film 103 so as to cover an inner wall of the via hole 102 by a sputtering method, and thereafter Cu 107 is deposited so as to be embedded in the via hole 102 by a plating method. Here, FIG. 7A shows a case where a long throw sputtering method is used as the sputtering method when the base film 106 is formed, FIG. 7B shows a case where a bias sputtering method is used, and FIG. 8 shows a case where a multistep sputtering method is used.

In the case of the long throw sputtering method (which is carried out without applying a substrate bias under the condition that the target power is between 10 kW and 20 kW and the pressure is 4×10⁻² Pa in the example in FIG. 7A), Ta is thickly deposited on a bottom surface of the via hole 102 and a portion (field portion) other than the via hole 102 of the insulating film 103, whereas scarce Ta is deposited on a sidewall surface of the via hole 102. As a result, due to insufficient coverage of the sidewall surface, poor embedding, for example, a void 108 occurs in copper 107 formed by plating.

In the case of the bias sputtering method (which is carried out under the condition that the target power is between 10 kW and 20 kW, the pressure is 4×10⁻² Pa, and the substrate bias is between 200 W and 500 W in the example in FIG. 7B), excessive Ta is deposited not only on the bottom surface of the via hole 102 but also in the vicinity of a rim portion of the via hole 102 (a so-called overhang is formed), which causes poor embedding, for example, a void 109 in the copper 107.

In the case of the multistep sputtering method (in which in a first step, long throw sputtering is carried out under the condition that the target power is between 10 kW and 20 kW, the pressure is 4×10⁻² Pa, and the substrate bias is between 0 W and 300 W, and in a second step, bias sputtering etching is carried out under the condition that the target power is between 0.2 kW and 5 kW, the pressure is between 3×10⁻¹ Pa and 7×10⁻¹ Pa, and the substrate bias is between 200 W and 500 W in the example in FIG. 8). Ta deposited on the bottom surface of the via hole 102 in the first step adheres again to a side surface of the via hole 102 to make up a shortage of Ta on the side surface, but on the other hand, if an etching factor is strong, Ta becomes insufficient on the bottom surface of the via hole 102. When positional displacement occurs between the lower wiring 101 and the via hole 102 due to this, for example, Cu deposited by plating diffuses into the insulating film.

Even if the various sputtering methods are used as described above, it is very difficult to form the basic film with a uniform film thickness in the opening. There is also a disadvantage that to control the film forming state of the base film causes complication of a film forming process thereof, resulting in an increase in the time required for the process. This causes an increase in target power consumption, an increase in particles produced at the time of film formation, and a deterioration in throughput, which leads to a considerably thick deposition on the field portion while the necessary amount of film is formed in the opening. The base film deposited on the field portion needs to be removed by polishing in a chemical mechanical polishing (CMP) process, but the base film too thick leads to a deterioration in throughput in the CMP process and furthermore exerts a bad influence on the capability of the entire manufacturing line. Moreover, CMP of the base film has chemical polishing as a strong factor, and hence flaws such as scratches easily occur, which may contribute to a reduction in the yield of wiring formation.

SUMMARY OF THE INVENTION

The present invention is made in view of the aforementioned problems, and its object is to provide a wiring structure forming method which can form a base film thin and uniformly on an inner wall surface, that is, from a sidewall surface to a bottom surface, of an opening without causing any disadvantage in terms of wiring formation by relatively simple steps to realize a highly reliable ultra-fine wiring structure, and a semiconductor device.

A wiring structure forming method of the present invention comprises the steps of: forming an opening in an insulating film over a substrate; forming a base film over the insulating film by a sputtering method in such a manner that the base film covers an inner wall surface of the opening; removing the base film over the insulating film other than that in the opening in such a manner that the base film remains only over the inner wall surface of the opening; and embedding a conductive material in the opening with the base film therebetween, and the base film is formed in such a manner that a film thickness thereof in a portion other than the opening over the insulating film is equal to or less than {fraction (1/20)} of a diameter of the opening.

A wiring structure forming method of the present invention comprises the steps of: forming an opening in an insulating film over a substrate; forming a base film by a sputtering method in such a manner that the base film covers only an inner wall surface of the opening and is not deposited over the insulating film other than that in the opening; and embedding a conductive material in the opening with the base film therebetween.

A wiring structure forming method of the present invention comprises the steps of: forming an opening in an insulating film over a substrate; and embedding a conductive material in the opening with a base film which covers an inner wall surface of the opening therebetween, and the base film is formed by a sputtering method under a condition of 1<Vd/Ve<2 where Vd/Ve is a ratio of a deposition rate (Vd) of a material for the base film to an etching rate (Ve) thereof.

A wiring structure forming method of the present invention comprises the steps of: forming an opening in an insulating film over a substrate; and embedding a conductive material in the opening with a base film which covers an inner wall surface of the opening therebetween, and the base film is formed by plural sputtering steps comprising:

-   -   a first step under a condition of Vd/Ve>1; and     -   a second step under a condition of Vd/Ve<1 where Vd/Ve is a         ratio of a deposition rate (Vd) of a material for the base film         to an etching rate (Ve) thereof.

A semiconductor device of the present invention comprises: a semiconductor substrate; an insulating film which is provided over the semiconductor substrate and in which an opening is formed; a base film which covers only an inner wall surface of the opening; and a conductive material which is embedded in the opening with the base film therebetween, and the base film is a sputtering film covering the inner wall surface at a uniform film thickness and made from a uniform material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a characteristic chart showing the quantitative relation between film formation time and a ratio (Vd/Ve) of a deposition rate (Vd) of sputtering particles and an etching rate (Ve) thereof in a bias sputtering process;

FIG. 2 is a characteristic chart showing the results of investigations of the relation between film formation time and film thickness inside and outside a via hole with a diameter of 0.1 μm in the bias sputtering process;

FIG. 3A and FIG. 3B are schematic sectional views each showing a state in which a base film is formed by a sputtering method of the present invention;

FIG. 4 is a characteristic chart showing film thickness in a field portion of a base film when the base film with a uniform film thickness is formed by a two-step bias sputtering method;

FIG. 5A and FIG. 5B are schematic sectional views showing a wiring forming method according to an embodiment in the order of steps;

FIG. 6A to FIG. 6C are schematic sectional views, subsequent to FIG. 5B, showing the wiring forming method according to the embodiment in the order of steps;

FIG. 7A and FIG. 7B are schematic sectional views each showing part of a process of forming wiring including a base film as a prior art; and

FIG. 8 is a schematic sectional view showing part of a process of forming wiring including a base film as a prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Basic Gist of the Present Invention

As described above, various conventional sputtering methods have a tendency to aim at realization of a base film with a thin and uniform film thickness by adding a film forming condition to a sputtering process or increasing the process and making the process more elaborate, for example, the application of a bias to a substrate or sputtering divided into plural steps. However, in the present circumstances, this inevitably causes the complication of the process, and moreover uniformity of the base film over the entire inner wall surface of an opening is not obtained. The present inventor changes his point of view from the aforementioned tendency to addition of the condition to the sputtering process to a microscopic state of sputtering, that is, a microscopic film forming state woven by a balance between deposition of sputtering particles and etching thereof in the sputtering process, quantifies this microscopic state, and pays attention to the correlation between this microscopic state and the film forming state of the entire base film.

The present inventor thinks that if, in the sputtering process, the sputtering condition is set so that the ratio of the deposition rate of sputtering particles to the etching rate thereof is within a certain range throughout the sputtering process, the thin and uniform base film can be formed over the entire inner surface of the opening even by one-step sputtering, and investigates the relation between film formation time and this ratio with a bias sputtering method as an example.

(One-Step Bias Sputtering)

FIG. 1 is a characteristic chart showing the quantitative relation between film formation time and a ratio (Vd/Ve) of a deposition rate (Vd) of sputtering particles and an etching rate (Ve) thereof in a bias sputtering process. Here, a general bias sputtering method is carried out under the condition that the target power is 10 kW, the pressure is 4×10⁻² Pa, and the substrate bias is 200 W, and bias sputtering etching is carried out under the condition that the target power is 0.5 kW, the pressure is between 3×10⁻² Pa and 7×10⁻¹ Pa, and the substrate bias is 200 W.

In a general bias sputtering method, the film is usually formed in the range of a Vd/Ve ratio of 2.5 or more to maintain a certain degree of film forming rate. In this range of Vd/Ve, the proportion of deposition is higher than that of etching, whereby the resputtering effect is small. In this case, to secure the coverage of a sidewall portion of the inner wall of the opening, it is necessary to increase the film formation time and substrate bias, but this causes adverse effects such as an increase in overhang, an increase in particles when the film is formed, and difficulty in reducing the thickness of the film.

In bias sputtering etching in a multistep sputtering method, to strengthen an etching factor, the range of a Vd/Ve ratio less than 1 (for example, approximately 0.75) is often selected. In this range, the contribution of Ta ions as a material for the film is small, and the etching effect by Ar ions is large, whereby film formation progresses in a state in which a film material is hardly deposited. This etching effect tends to increase as the pressure at the time of film formation (pressure of an Ar atmosphere) becomes higher, and film peeling in a rim portion of the opening and film peeling in a bottom portion of the opening increase, whereby there arises the high possibility of causing failures such as Cu diffusion into an insulating film caused by a wiring short-circuit and positional displacement of the opening, respectively.

As a result of forming the base film by the one-step bias sputtering within the range of a Vd/Ve ratio not less than 1 nor more than 2.5, the present inventor finds that if the ratio is controlled to be 1<Vd/Ve<2 throughout the formation of the film, the thin and uniform base film over the entire inner wall surface of the opening is obtained. Namely, in this case, the supply of Ta ions and resputtering by Ar ions are balanced, local etching in the rim portion and the bottom portion of the opening is prevented, and a certain amount of Ta is secured even in the bottom portion. Moreover, reinforcement of the film thickness on the sidewall of the opening by the resputtering effect moderately progresses, and as a result, the thin and uniform base film over the entire inner wall surface of the opening is obtained.

Here, to obtain 1<Vd/Ve<2 throughout the formation of the film, it is suitable to carry out sputtering under the condition that the target power is a relatively low power between 0.1 kW and 5.0 kW, the pressure of an atmosphere of sputtering ion species (Ar in this case) is between 1×10⁻² Pa and 1×10⁻¹ Pa, and the substrate bias is between 100 W and 450 W, and in this example, the target power is set at 5 kW, the pressure is set at 6×10⁻² Pa, and the substrate bias is set at 300 W. As described above, in this example, a desired base film shape is attained by a smaller sputtering amount than in prior arts by low power in the one-step bias sputtering, and as a result effects such as reductions in wiring resistance and contact resistance, a reduction in target power consumption, an increase in throughput, and a reduction in particles at the time of film formation are produced.

Moreover, the present inventor compares a film thickness on the inner wall surface of the opening of the base film and a film thickness on the field portion under the sputtering condition which satisfies 1<Vd/Ve<2 throughout film formation.

FIG. 2 is a characteristic chart showing the results of investigations of the relation between film formation time and film thickness inside and outside a via hole with a diameter of 0.1 μm in the bias sputtering process. Here, the general bias sputtering method is carried out under the condition that the target power is 10 kW, the pressure is 4×10⁻² Pa, and the substrate bias is 200 W, and sputtering of the present invention is carried out under the condition that the target power is 5 kW, the pressure is 6×10⁻² Pa, and the substrate bias is 300 W.

It turns out that in the general bias sputtering method, the film thickness of the base film on the field portion is larger than that on the inner wall surface of the via hole, whereas in this example, the film thickness of the base film on the inner wall surface of the via hole is formed larger than that on the field portion, an increase in film thickness on the field portion with the progress of film formation is slight, and that the film thickness on the field portion is kept below 5 nm. In other words, this means that the film thickness of the base film on the field portion is equal to or less than {fraction (1/20)}, more preferably {fraction (1/30)} of the diameter (0.1 μm in this case) of the via hole. Moreover, it means that the film thickness of the base film on the field portion is between 20% and 100% of the film thickness on the inner wall of the via hole, and approximately 20% in this case. Further, it is confirmed that the state of embedding of Cu in the via hole in this film formation range is satisfactory.

Furthermore, the present inventor thinks out that according to the aforementioned experimental results, under a predetermined sputtering condition satisfying 1<Vd/Ve<2, the thin and uniform base film is formed only on the entire inner wall surface of the opening, and on a portion on the insulating film other than the opening, that is, on the field portion, the supply of Ta ions and resputtering by Ar ions are nearly equal, so that a state in which the deposition amount of Ta ions becomes zero is obtained. In this case, only Cu on the field portion is required to be removed by polishing in a CMP process subsequent to Cu deposition, which can reduce a polishing process of the base film.

Specifically, a state in which the base film is formed by the sputtering method of the present invention is shown in FIG. 3A and FIG. 3B.

As shown in FIG. 3A, after a via hole 102 to connect a lower wiring 101 and an upper wiring not shown is formed in an insulating film 103 using an etching stopper film 104 and a hard mask 105, a base film 111 made from Ta is formed on the insulating film 103 so as to cover an inner wall of the via hole 102 by a one-step low-power bias sputtering method of the present invention. Thus, the base film 111 with a thin and uniform film thickness covering a region from an inner wall surface of the via hole 102 to the insulating film 103 is obtained. Thereafter, Cu 107 is deposited so as to be embedded in the via hole 102 by a plating method. Any void and the like do not occur in the via hole 102 and so on even if the Cu 107 is embedded, leading to the realization of satisfactory Cu deposition.

Moreover, as shown in FIG. 3B, by selecting the sputtering condition within the range satisfying 1<Vd/Ve<2, it is possible that the base film 111 with the thin and uniform thickness is formed so as to cover only the inner wall of the via hole 102 without the film material being deposited on the field portion. Here, in order that only the via hole 102 is filled with the Cu 107 after the Cu 107 is deposited so as to be embedded in the via hole 102, in the example in FIG. 3A, it is necessary to remove the Cu 107 and the base film 111 on the field portion in sequence by polishing by the CMP method, but in the example in FIG. 3B, since the base film 111 does not exist on the field portion, only the Cu 107 on the field portion is required to be removed by polishing by the CMP method, whereby the CMP process of the base film 111 can be reduced.

(Multistep Sputtering)

In the present invention, also by multistep sputtering in addition to the aforementioned one-step bias sputtering, it is possible that the base film with a thin and uniform thickness is formed on the inner wall surface of the opening, and that the film thickness on the field portion is formed to be equal to or less than {fraction (1/20)} (more preferably equal to or less than {fraction (1/30)}) of the diameter of the opening.

FIG. 4 is a characteristic chart showing the film thickness on the field portion of the base film when the base film with a uniform film thickness is formed by a two-step bias sputtering method. Here, a second step is carried out under the condition that the target power is 2.5 kW, the pressure is between 4×10⁻² Pa and 8×10⁻² Pa, and the substrate bias is 300 W or under the condition that the target power is 0.5 kW, the pressure is between 4×10⁻² Pa and 8×10⁻² Pa, and the substrate bias is 200 W.

In this example, in a first step, the film with a film thickness approximately between 5 nm and 10 nm is formed under the sputtering condition of Vd/Ve>1, and in the second step, sputtering etching is carried out under the sputtering condition of Vd/Ve<1. Consequently, the base film with the thin and uniform film thickness is formed on the inner wall surface of the via hole, and the film thickness on the filed portion is kept below 5 nm, and hence it turns out that an effect equal to that by the one-step bias sputtering method of the present invention can be obtained.

Specific Embodiment of the Present Invention

A specific embodiment in which the present invention is applied to the formation of Cu wiring (and via connection) by a damascene method will be explained below.

FIG. 5A and FIG. 5B and FIG. 6A to FIG. 6C are schematic sectional views showing a wiring forming method according to this embodiment in the order of steps.

First, as shown in FIG. 5A, after a semiconductor element such as a MOS transistor is formed on a semiconductor substrate not shown, a lower wiring 1 is formed to be connected to the semiconductor element. Subsequently, an etching stopper film 2 with a film thickness of a few tens of nm is formed on the lower wiring 1, for example, using a material such as SiO+SiC, and thereafter, an interlayer insulating film 3 with a film thickness of a few hundreds of nm is formed on the etching stopper film 2 using an organic or inorganic insulating material by an SOG method or a CVD method. Then, after a hard mask 4 having an opening is formed on the interlayer insulating film 3, for example, by using a material such as SiO+SiC, a via hole 5 with a diameter approximately between 0.1 μm and 0.15 μm and a depth approximately between 300 nm and 700 nm is formed in the interlayer insulating film 3 by dry etching with the hard mask 4. CF based gas, NH₃ base gas, or N₂/H₂ gas is used as etching gas. At this time, an opening is also formed in the etching stopper film 2, and the surface of the lower wiring 1 is exposed from a bottom surface of the lower wiring 1.

Subsequently, as shown in FIG. 5B, one-step bias sputtering is carried out under the sputtering condition which satisfies 1<Vd/Ve<2 and under which a film material is not deposited on a field portion, and here the target power is between 0.2 kW and 5 kW, the pressure is 4×10⁻² Pa, and the substrate bias is between 150 W and 450 W. By performing sputtering with Ta as a material under this condition, Ta is (hardly) deposited on the interlayer insulating film 3 (field portion) other than that in the via hole 5 but deposited only on an inner wall surface of the via hole 5, and a base film 6 with a uniform film thickness of 5 nm or less is formed. It is also possible here to use at least one type of refractory metal selected from the group consisting of Ti, W, Zr, and V or a nitride of these metals in place of Ta as a sputtering material. Moreover, it is defined that a preliminary step of this film forming step includes an electric discharge starting step, an electric discharge stabilizing step, an electric discharge completing step, and a substrate electricity removing step. Incidentally, there is a possibility that the substrate electricity removing step is not included.

Thereafter, as shown in FIG. 6A, a seed metal film 7 is formed with Cu as a material on the interlayer insulating film 3 by sputtering so as to cover the inner wall surface of the via hole 5 with the base film 6 between them. The seed metal film 7 with a film thickness approximately between 40 nm and 150 nm is formed under the sputtering condition that the target power is between 5 kW and 30 kW, the pressure is between 1×10⁻⁵ Pa and 10 Pa, and the substrate bias is between 200 W and 500 W. Here, it is also possible to use a Cu alloy containing Al, Ti, Zr, Ni, Ag, Pd, and so on in place of Cu as a material for the seed metal film 7.

Subsequently, as shown in FIG. 6B, Cu 8 is embedded in a wiring trench 12 by the plating method with the seed metal film 7 as an electrode. On this occasion, the Cu 8 with a film thickness approximately between 500 nm and 2000 nm is deposited at a current density between 7 A/cm² and 30 A/cm² with a copper sulfate bath.

Then, as shown in FIG. 6C, the Cu 8 is removed by polishing by the CMP method with an organic acid slurry solution and, for example, the hard mask 4 as a stopper, and a via-plug 9 which is made by filling the via hole 5 with the Cu 8 with the base film 6 therebetween is formed. At this time, Ta of the base film 6 does not exist on the field portion, whereby only polishing of the Cu 8 is needed.

Thereafter, a wiring structure is completed through the formation of another interlayer insulating film not shown and an upper wiring not shown which is connected to the via-plug 9.

Incidentally, also when the lower wiring 1 is formed, it is also possible to form a base film which thin and uniformly covers an inner wall of a wiring trench formed in an insulating film by sputtering technology of the present invention and embed Cu in this wiring trench with the base film therebetween by a damascene method.

Moreover, in this embodiment, the case where the sputtering technology of the present invention is used for the formation of the base film of the via-plug in the damascene method is shown as an example, but the present invention is not limited to this case, and, for example, it is also possible that the present invention is applied to a dual damascene method, and that a base film with a thin and uniform film thickness is formed by the aforementioned sputtering method so as to cover the inner wall surface from a via hole to a wiring trench and at the same time Cu is embedded in the via hole and the wiring trench to thereby form a wiring structure.

As explained above, according to this embodiment, it becomes possible to form a base film thin and uniformly in an opening, in this case, on an inner wall surface, that is, from a sidewall surface to a bottom surface, of the via hole 5 without causing any disadvantage in terms of wiring formation by relatively simple steps, and improvements in wiring resistance and contact resistance, lowering of load and a reduction in the CMP process, a reduction in target power consumption, an increase in throughput, a reduction in particles at the time of film formation, an increase in wiring performance, and an increase in manufacturing line capability are attained to thereby realize a highly reliable ultra-fine wiring structure.

According to the present invention, it becomes possible to form a base film thin and uniformly on an inner wall surface, that is, from a sidewall surface to a bottom surface, of an opening without causing any disadvantage in terms of wiring formation by relatively simple steps, and improvements in wiring resistance and contact resistance, lowering of load and a reduction in the CMP process, a reduction in target power consumption, an increase in throughput, a reduction in particles at the time of film formation, an increase in wiring performance, and an increase in manufacturing line capability are attained to thereby realize a highly reliable ultra-fine wiring structure.

The present embodiments are to be considered in all respects as illustrative and no restrictive, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. 

1. A wiring structure forming method, comprising the steps of: forming an opening in an insulating film over a substrate; forming a base film over the insulating film in such a manner that the base film covers an inner wall surface of the opening by a sputtering method; removing the base film over the insulating film other than that in the opening in such a manner that the base film remains only over the inner wall surface of the opening; and embedding a conductive material in the opening with the base film therebetween, wherein the base film is formed in such a manner that a film thickness thereof in a portion other than the opening over the insulating film is equal to or less than {fraction (1/20)} of a diameter of the opening.
 2. The wiring structure forming method according to claim 1, wherein the base film is formed in such a manner that a film thickness thereof in a portion other than the opening over the insulating film is equal to or less than {fraction (1/30)} of a diameter of the opening.
 3. The wiring structure forming method according to claim 1, wherein the base film is formed in such a manner that a film thickness thereof over a bottom surface of the inner wall surface of the opening is not less than 20% nor more than 100% of a film thickness in a portion other than the opening over the insulating film.
 4. A wiring structure forming method, comprising the steps of: forming an opening in an insulating film over a substrate; forming a base film in such a manner that the base film covers only an inner wall surface of the opening and is not deposited over the insulating film other than that in the opening by a sputtering method; and embedding a conductive material in the opening with the base film therebetween.
 5. The wiring structure forming method according to claim 1, wherein the base film is formed by the sputtering method under a condition of 1<Vd/Ve<2 where Vd/Ve is a ratio of a deposition rate (Vd) of a material for the base film to an etching rate (Ve) thereof.
 6. The wiring structure forming method according to claim 1, wherein the base film is formed by plural sputtering steps comprising: a first step under a condition of Vd/Ve>1; and a second step under a condition of Vd/Ve<1 where Vd/Ve is a ratio of a deposition rate (Vd) of a material for the base film to an etching rate (Ve) thereof.
 7. The wiring structure forming method according to claim 5, wherein the base film is formed so as to cover only the inner wall surface of the opening and not to be deposited over the insulating film other than that in the opening.
 8. The wiring structure forming method according to claim 1, wherein when the base film is formed, a bias voltage is applied to the substrate.
 9. The wiring structure forming method according to claim 8, wherein the base film is formed under a condition that a target power is not less than 0.1 kW nor more than 5.0 kW and a bias voltage is not less than 100 W nor more than 450 W.
 10. The wiring structure forming method according to claim 1, wherein the base film is formed under a condition that a pressure of an atmosphere of a sputtering ion species is not less than 1×10⁻² Pa nor more than 1×10⁻¹ Pa.
 11. The wiring structure forming method according to claim 1, wherein the conductive material is copper or a conductive substance containing copper, and the opening includes at least a connection hole.
 12. The wiring structure forming method according to claim 1, wherein a material for the base film is at least one type selected from the group consisting of tantalum, titanium, tungsten, zirconium, and vanadium or a nitride containing the at least one type.
 13. A semiconductor device, comprising: a semiconductor substrate; an insulating film which is provided over said semiconductor substrate and in which an opening is formed; a base film which covers only an inner wall surface of the opening; and a conductive material which is embedded in the opening with said base film therebetween, wherein said base film is a sputtering film covering the inner wall surface at a uniform film thickness and made from a uniform material.
 14. The semiconductor device according to claim 13, wherein said conductive material is copper or a conductive substance containing copper, and the opening includes at least a connection hole.
 15. The semiconductor device according to claim 13, wherein a material for said base film is at least one type selected from the group consisting of tantalum, titanium, tungsten, zirconium, and vanadium or a nitride containing the at least one type. 